1. Field of the Invention
The present invention relates to the shaping of sheets of thermoplastic material, most particularly, those of glass. Many techniques for shaping glass sheets are known. Perhaps the simplest technique involves heating a glass sheet while supported on a contoured mold of outline configuration and to permit the sheet to sag by gravity as it is heated so that it conforms to the outline shape of the mold.
It often is desirable to speed the shaping process by applying a mechanical bending force such as by sandwiching the glass sheets in pressurized engagement between a pair of contoured shaping molds. For such shaping, glass sheets are sometimes suspended by tongs and at other times are supported in a horizontal plane.
2. Technical Background And Description Of Patents Of Interest
When glass sheets are shaped after being conveyed into a shaping station, the position and alignment of the glass sheet with respect to the shaping molds is very important. Consequently stop means have been used to align the position of the glass sheet relative to a pair of shaping molds so as to insure that the glass sheet is shaped into the desired contour. However, if a glass sheet that engages stop means to be properly aligned between a pair of shaping molds is permitted to have its edge scrape against the stop member when a shaping mold moves the glass sheet in the direction of the glass sheet thickness to shape the sheet, the edge is liable to become distorted. The distorted edge makes it difficult to install the shaped glass sheet within a frame designed to receive the glass sheet of a desired configuration.
It has been the custom in the past to provide means that move stop means into glass edge engaging position to insure that each glass sheet arrives at a position of proper alignment within the shaping station and that retract the stop means from engagement with the glass sheet edge before the heat softened glass sheet is moved in the direction of its thickness on one of the shaping molds. In the past, the stop means was actuated by electrically controlled actuation means and it was sometimes difficult to maintain proper timing to coordinate the movement of the stop means with the movement of the shaping molds.
Examples of patents that show independent actuation of stop means relative to the operation of shaping molds include U.S. Pat. Nos. 3,265,484 to Ritter, 3,315,774 to Leflet, 3,338,695 and 3,361,552 to Ritter, 3,459,526 to Stickel et al., 3,468,645 to McMaster et al., 3,476,541 and 3,476,542 to Ritter, 3,485,615 to Rahrig et al., 3,485,618 to Ritter, 3,488,178 to Welker et al., 3,527,589, 3,554,724 and 3,563,721 to Ritter, 3,573,889 to McMaster et al., 3,615,338 to Boyles, 3,676,098 to Hall, 3,734,706 to Ritter, 3,905,794 to Revells et al., 3,960,535 to Hamilton, 4,043,782 to Bamford, 4,074,996 to Hagedorn et al., 4,119,427 to Revells, and 4,217,126, 4,305,745 and 4,312,661 to Hagedorn et al.
The previous patents are all characterized by requiring some type of complicated timing mechanism to coordinate the movement of the stop means with the movement of the glass sheet into a shaping station. The last Hagedorn et al. U.S. Pat. No. 4,312,661 also discloses an articulated pressing mold having pivotal end sections and mechanical means interconnecting the end mold sections to coordinate their movements in unison.
U.S. Pat. No. 4,229,200 to Seymour discloses fixedly located stop members of a shape conforming to the leading edge of a glass sheet of non-rectangular outline that moves into a shaping station. The glass sheet is supported on a gaseous bed and is lifted by a vacuum holder or a lifting ring into engagement by a vacuum holder at a shaping station. Since the stop means are located in fixed position, although their positions may be adjusted and they may be replaced for different patterns, the glass sheet tends to scrape against the fixed stop members when it is lifted into engagement with the vacuum holder either by vertical movement of a vacuum holder engaging the upper surface of the glass sheet by vacuum or by a mechanical lifting ring that engages the lower surface of the glass sheet to bring it into engagement with the vacuum holder disposed above the portion of the gaseous bed that is beneath the vacuum holder.
U.S. Pat. No. 4,252,552 to Frank and U.S. Pat. No. 4,282,026 to McMaster et al disclose the use of sensors that detect the presence of a glass sheet and cooperate with timing circuits to coordinate the position of the glass sheet and the press shaping molds. Control circuits of this type are expensive and require high caliber personnel to maintain whenever things go wrong with such equipment.
U.S. Pat. No. 4,272,275 to Reese discloses gravity actuated members that engage glass edges in the vicinity of an outline mold. Support means temporarily support the glass edge engaging members to locate the upper edges of the glass edge engaging members in position to abut the edge of one or more glass sheets as the latter sag toward the outline mold and suddenly and automatically release their supporting force to remove the glass edge engaging members from the vicinity of the edge of the supported glass sheets just before the glass sheets are lifted from the outline mold and supported in sandwiched relation between an upwardly rising mold which is one of a pair of molds and an upper mold of complementary curvature to the lower shaping mold. While this invention mechanically coordinates the termination of the edge engagement with the lifting of a glass sheet off an outline mold, it is necessary to reset the supporting elements for the glass engaging members before each time a glass sheet is loaded onto a mold of outline configuration provided with this type of glass edge engaging members.
It would be desirable for the glass sheet shaping art to develop glass edge engaging members that need not be reset manually between shaping operations, particularly in the type of glass sheet bending operation depicted in U.S. Pat. Nos. 4,229,200 to Seymour or 4,252,552 to Frank or 4,282,026 to McMaster et al.